The present invention generally relates to information signal recording mediums and reproducing apparatuses therefor, and more particularly to an information recording medium which is recorded with picture element data amounting to a total of one field which is formed from arbitrary picture element data in first and second fields which make up one frame of a digital video signal, and a reproducing apparatus therefor. The reproducing apparatus is designed to reproduce the second field in a sequence different from a sequence with which the recorded picture element data are reproduced from the information recording medium in the first field.
Recently, systems which record a digital video signal obtained by subjecting video and audio signals to digital pulse modulation such as pulse code modulation (PCM) and a digital audio signal onto a rotary recording medium (hereinafter simply referred to as a disc) as variations in geometrical configuration, and reproduce the recorded signal as variations in the intensity of light reflected from the disc or variations in electrostatic capacitance, have been developed and realized. Further, recording systems have been proposed for digital audio discs, according to which a digital video signal comprising color still picture information is added to a digital audio signal and recorded together on the same track on the disc. Generally, a plurality of music programs are recorded on the same side of such a digital audio disc, and the digital video signal comprising the color still picture information is recorded in correspondence with each of the recorded music programs. When reproducing such a digital audio disc, the music programs on the disc can be reproduced by a reproducing system which is common throughout the world.
However, the television systems are not common throughout the world, and there roughly exist three kinds of television systems. Accordingly, in order to enable reproduction of the video signal recorded on the disc even if the television system employed in a region or country is different from the television system of the recorded video signal, it is first necessary to convert the recorded video signal into a signal format in accordance with the television system of the reproducing apparatus used in that region or country before obtaining a reproduced picture. The information content of the above digital video signal relates to a color still picture which helps the listener's imagination when he listens to the reproduced sounds of the digital audio signal. Hence, it is desirable to reproduce the digital video signal from the disc in the signal formats which are in accordance with each of the television systems, regardless of the differences in the television systems throughout the world.
The color television systems throughout the world can be divided roughly into three systems, that is, NTSC, PAL, and SECAM systems, according to the transmission formats of the chrominance signal. In each of these color television systems, the color video signal is constituted by a luminance signal and two kinds of color difference signals. Hence, it is desirable to employ a component coding system which transmits the color video signal by independently subjecting the luminance signal and the two kinds of color difference signals to digital pulse modulation, in order to facilitate compatibility between the three systems. Moreover, it is desirable to employ the component coding system in view of the fine picture quality which may be obtained by use of a display monitor having input terminals for the three primary colors of red (R), green (G), and blue (B) which will probably be realized in the future, and especially because partial moving pictures may be recorded on the digital audio discs, and the like.
The frequency band of the luminance signal within the television broadcasting signal, is 4.2 MHz in the NTSC system, and 5 MHz or 6 MHz in the PAL and SECAM systems. However, the frequency band of the luminance signal which is actually transmitted and used in the television receiver is up to approximately 3 MHz in the NTSC system, and up to a range of 3 MHz to 4 MHz in the PAL and SECAM systems. Accordingly, it is possible to lower the sampling frequency to approximately 8 MHz, although it is preferable to reserve a certain margin.
Thus, if the sampling frequency of the luminance signal is selected to 9 MHz, and the sampling frequencies of the two kinds of color difference signals (R-Y) and (B-Y) are each selected to 2.25 MHz which is 1/4 the frequency of 9 MHz, the number of sampling points of the luminance signal in one scanning line, becomes equal to 576 (=(9.times.10.sup.6)/(15.625.times.10.sup.3)). However, these sampling points include the horizontal blanking periods such as the horizontal synchronizing signal intervals and the color burst signal intervals. Hence, if the sampling points in these horizontal blanking periods are excluded from the sampling points of the luminance signal, the number of sampling points of the luminance signal in one scanning line may be reduced to approximately 456.
On the other hand, a generally marketed 54k RAM has 2.sup.16 (=65,536) bits. Thus, 2.sup.18 (=4.times.2.sup.16 =262,144) bits are obtainable is four of such 64k RAMs are used. If this number 2.sup.18 is divided by 456 which is the number of effective sampling points of the luminance signal in one scanning line, the quotient becomes approximately equal to 574.87. Hence, if the number of effective scanning lines among the 625 scanning lines in one frame, which are transmitted as a picture, is selected to 572 which is exceedingly close to the number 574.87 but is less than 574.87 as previously proposed in a U.S. patent application Ser. No. 485,054 filed Apr. 14, 1983 entitled "DIGITAL VIDEO SIGNAL RECORDING SYSTEM AND REPRODUCING APPARATUS" (now U.S. Pat. No. 4,520,401) in which the assignee is the same as the assignee of the present application, each picture element data of the effective sampling points of the luminance signal in one frame can be efficiently stored by use of four 64k RAMs.
The information quantity of the two kinds of color difference signals which are obtained by independently subjecting the two kinds of color difference signals (R-Y) and (B-Y) at the sampling frequency of 2.25 MHz, is 1/4 the information quantity of the above digital luminance signal. The picture element data of the effective sampling points of one of the two color difference signals can thus be efficiently stored in one 64k RAM. Accordingly, if the picture element data of one sampling point is represented by six bits, one frame of the digital video signal in which the digital luminance signal and the two kinds of color difference signals are time-sequentially multiplexed, can be stored by use of thirty-six (=6.times.(4+1 +1)) 64k RAMs.
Generally, the digital video signal reproducing apparatus only comprises field memories. Further, the video signal corresponding to only one of the two fields in one frame, is recorded on the disc. Conventionally, when only the digital video signal of one field is transmitted, only the data related to the picture elements of one of first and second fields in one frame are transmitted among 114.times.4 picture elements in the scanning direction (horizontal direction) and 572 picture elements in the vertical direction which make up one frame. The number 114.times.4 is for the case of the luminance signal, and the picture elements in the scanning direction is 114 in the case of the color difference signal (R-Y) or (B-Y). Therefore, compared to the case where the video signal of one frame is transmitted, the vertical resolution of the reproduced picture inevitably became poor, and aliasing noise increased. In addition, jitter was introduced in the vertical direction of the picture, and oblique lines in the picture obtained by reproducing the transmitted signal, were reproduced in the form of steps. Furthermore, when horizontal lines which differ in their widths and positions existed in the picture, there was a problem in that such horizontal lines were reproduced with the differences overemphasized.